On Thu, Jul 15, 2004 at 08:34:18PM -0600, Rich Adamson wrote: > > I've been following the list for months, and I have a working Asterisk > > setup, but it'd be *really* useful to me at this point if someone could > > summarize when Asterisk has echo problems and when it doesn't. For > > instance, I usually hear a far-end echo when talking on my 7940, but > > not when using a POTS phone plugged into a TDM400 FXO port. It doesn't > > seem to matter if the call goes out over a POTS line or via NuFone; > > either way there's a fair bit of echo on most (but not all) calls. > > > > Do different SIP phones have better echo cancellation then the Cisco > > 7940/60s? How about the Polycom IP500/600s? > > > > Does it matter if calls go out via POTS/T-1/PRI/VoIP? > > > > The general impression that I've received is that "fast" channels > > (basically traditionally telephony interfaces) don't exhibit noticeable > > echo, but the slight delay associated with VoIP packetization unmasks > > existing echo. Is that a reasonable summary? > > > > We're starting to plan for a new office build-out at work, and I'd love > > to use Asterisk and SIP phones in the new office, but I'm not going to > > try to sell management on a phone system with a horrible echo problem, > > even if it will get fixed eventually. > > For the most part, echo is less of a problem today then what it was > a month or so ago. The source of the echo varys case by case, however > key points that need to be addressed in _any_ installation include: > - * fxo pstn interface cards (eg, x100p, tdm-fxo) have to be configured > to match the impedance of the telco standard for whatever country > you're in. The x100p, by design, appears to be limited to a 600 ohm > telco impedance (US standard), and will likely generate echo when > attached to pstn lines that are not 600 ohms. The tdm cards are > different and can be configured to match just about any telco standard > worldwide. (Don't know about the x101p, never seen one.) > - echo issues with the zap interfaces (eg, x100p, tdm, T1/E1 cards) > rely on a software echo canceler within asterisk. If the above > impedance match is correct, most implementations seem to have found > parameters that minimize echo for them. However, there are still some > in which echo is a problem and best 'guess' as of this afternoon is > those cases appear to have something to do with undocumented internal > system hardware. Some folks have found swapping a motherboard for > another with no other changes reduces echo by noticable amounts. > That would suggest buss speed, PCI version, or something like that > other then processor speed or RAM. There are working examples of > 300 mhz machines with no echo, 2.2 ghz machines with echo, and dual > processor systems with echo. > - Digital interfaces to * (eg, T1/E1, PRI, ISDN) tend to be less prone > to echo, however there are some implementations that still have it > and non-technical users of those systems do complain. Technical > users tend to tune it out. > - there has been very little list noise associated with echo that > could be honestly pinned on any sip phone. > - there's been a lot of opinions stated about the cause of echo on > the list, and at least some have no technical factual basis. > - there's a rather strong belief that additional echo problems exist > within asterisk, and a group of non-programmer types are attempting > to isolate common items in an effort to document the problem for > those that have the programming skills to address. (That's happening > on a non-asterisk email list.) > > It seems that production systems either don't have any echo issues, or > they have objectionable amounts. There does not seem to be anything > in between. Its probably fair to say the majority (if no all) developers > don't have the problem, making it most difficult to isolate and > troubleshoot the cause. > > Best guess (based only on the list noise level since Octomber 2003) is > that probably 80% of the production * systems are near echo free, and > 20% still have objectionable echo. Others may argue a different ratio. > YMMV. > > Rich >
Well, I must be among that 20%. I have annoying echo on PRI lines and have tried everything available to mitigate the problem, with no success. I am a programmer with sufficient technical skills to attack the problem. HOWEVER, I am not about to spend the time it would take to decipher zaptel.c all by myself. I OFFER to PAY someone who has an understanding of zaptel.c to help me with this problem. Any takers out there??? [EMAIL PROTECTED] > > _______________________________________________ > Asterisk-Users mailing list > [EMAIL PROTECTED] > http://lists.digium.com/mailman/listinfo/asterisk-users > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
